Data gathering device for a rack enclosure

ABSTRACT

A data gathering device for a rack enclosure which is, in use, cooperable with at least one SES processor, each processor being incorporated in a respective plug-in card. The data gathering device comprises at least one port adapted to communicate with a respective environmental services processor, a plurality of data inputs and a plurality of controllable outputs. The data gathering device is adapted to generate and send, to an SES processor responsible for the enclosure, a message reporting the state of the data inputs and to receive, from the responsible SES processor, a message including a command determining the state of one of the controllable outputs.

RELATED APPLICATIONS

This application relates to co-pending application no. S2000/0707 filedon Sep. 7, 2000 entitled “A Protocol for a Power Supply Unit Controller”naming Barrie Jeremiah Mullins et al as inventors; to co-pendingapplication no. S2000/0708 filed on Sep. 7, 2000 entitled “ImprovedPower Supply Unit Controller” naming Barrie Jeremiah Mullins et al asinventors; to co-pending application no. S2000/0709 filed on Sep. 7,2000 entitled “Performance Monitoring in a Storage Enclosure” namingAedan Diarmid Cailean Coffey et al as inventors; to co-pendingapplication no. S2000/0710 filed on Sep. 7, 2000 entitled “Fibre ChannelDiagnostics in a Storage Enclosure” naming Aedan Diarmid Cailean Coffeyet al as inventors; and to co-pending application no. S2000/0711 filedon Sep. 7, 2000 entitled “CrossPoint Switch for a Fibre ChannelArbitrated Loop” naming Aedan Diarmid Cailean Coffey as inventor.

FIELD OF THE INVENTION

The present invention relates to a data gathering device for monitoringenvironmental parameters within a rack enclosure housing one or morestorage devices.

BACKGROUND OF THE INVENTION

In a rack enclosure comprising a backplane into which a number ofdevices such as storage devices and/or an associated controller as wellas power supplies and fans are connected, monitoring environmentalconditions is important so that errors or potential failure of a systemcan be detected as soon as possible. This helps to maintain the highavailability of data required of storage subsystems. Environmental datamay be gathered directly from devices, such as fans or power supplies toindicate their presence/absence and their operating state, or from oneor more thermometers to indicate if an enclosure is overheating for somereason. Within the rack enclosure environmental condition indicatorsinclude LED's, buzzers etc.

For rack enclosures housing Small Computer Systems Interface (SCSI)devices based on media such as parallel SCSI or Fibre-Channel, enclosureservices protocols have been developed enabling a controller housedwithin a rack enclosure to reliably communicate environmentalinformation with a host systems management application, enabling remotemonitoring and control of a rack enclosure. This system's managementapplication then notifies an operator in the event of a failed componentor any other preconfigured alarmed event.

Such conventional environmental monitoring typically includes all theenvironmental monitoring hardware, including an enclosure managementcontroller on a plug-in card, thus there are very high pin count (andexpensive) connectors between the backplane and the monitoring deviceslocated around the rack enclosure. As rack enclosures get bigger andmore complex this problem gets worse and worse.

If on the other hand, environmental monitoring hardware is includedexclusively on the backplane, any failure means that the system must bebrought down to replace the backplane, and this may be intolerable froman availability point of view.

DISCLOSURE OF THE INVENTION

According to the present invention there is provided a data gatheringdevice for a rack enclosure which is, in use, cooperable with at leastone environmental services processor, each processor being incorporatedin a respective plug-in card, said data gathering device comprising atleast one port adapted to communicate with a respective environmentalservices processor, a plurality of data inputs and a plurality ofcontrollable outputs, said data gathering device being adapted togenerate and send, to a one of said at least one environmental servicesprocessors responsible for said enclosure, a message reporting the stateof said data inputs and to receive, from said responsible environmentalservices processor, a message including a command determining the stateof one of said controllable outputs.

In a second aspect of the invention there is provided a backplane for arack enclosure, said backplane including one or more data gatheringdevices, each data gathering device being, in use, cooperable with atleast one environmental services processor, each processor beingincorporated in a respective plug-in card, each data gathering devicecomprising at least one port adapted to communicate with a respectiveenvironmental services processor, a plurality of data inputs and aplurality of controllable outputs, each data gathering device beingadapted to receive an instruction from a one of said at least oneenvironmental services processors responsible for said enclosure to takeresponsibility for data gathering, said data gathering device beingadapted, when responsible for said enclosure, to generate a messagereporting the state of said data inputs to said responsibleenvironmental services processor and to receive a message including acommand from said responsible environmental services processordetermining the state of one of said controllable outputs.

In a further aspect of the invention there is provided a rack enclosuresystem comprising a backplane including one or more data gatheringdevices and at least one plug-in card incorporating a respectiveenvironmental services processor, each data gathering device comprisingat least one port adapted to communicate with a respective environmentalservices processor, a plurality of data inputs and a plurality ofcontrollable outputs, each data gathering device being adapted toreceive an instruction from a one of said at least one environmentalservices processors responsible for said enclosure to takeresponsibility for data gathering, said data gathering device beingadapted, when responsible for said enclosure, to generate a messagereporting the state of said data inputs to said responsibleenvironmental services processor and to receive a message including acommand from said responsible environmental services processordetermining the state of one of said controllable outputs.

Preferably, said backplane is adapted to receive fibre channel storagedevices and said data gathering device includes at least one portadapted to communicate with a respective one of said storage devices,said data gathering device being adapted to relay environmental servicesrequests from a host application received via a storage device to saidresponsible environmental services processor and to relay responses fromsaid responsible environmental services processor to said storagedevice.

Preferably, said data gathering device includes two ports, each adaptedto communicate with a respective one of two environmental servicesprocessors.

The present invention mitigates the problems of the prior art by puttingdata gathering and control functions on the backplane, thus replacingmany signal lines with, for example, a three wire serial bus. By movingthe data gathering function to the backplane the pin count of theconnectors can be significantly reduced.

Thus, using the invention connector costs are reduced for shelves of asimilar size. Alternatively, since the shelves are always gettingbigger, the invention allows more modules to be integrated together onone card with a similar connector size.

The invention offers a high degree of flexibility based on populationoptions thus requiring minimal duplicate software and even hardwaredevelopment.

In the preferred embodiment, the backplane is adapted to receive twoenclosure services cards, each connected to a respective data gathererdevice and cross-connected to another data gatherer device. This meansthat in spite of introducing data gathering circuitry onto thebackplane, no single point of failure is introduced. Nonetheless, shouldthis level of redundancy not be required, then only one data gathererdevice socket need be populated on the backplane and only one enclosureservices card need be provided for the backplane.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompany drawings, in which:

FIG. 1 is a block diagram illustrating a backplane incorporating a pairof data gathering devices according to the present invention.

DESCRIPTION OF THE PREFERRED-EMBODIMENT

Referring now to FIG. 1, where a preferred embodiment of the inventionis illustrated, a backplane 10 suitable for being housed in a 19″ 3Urack/shelf is shown schematically. For clarity, detail such as trackingor peripheral devices such as memory chips have been omitted where thisdetail is not necessary for describing the present invention.

In the preferred embodiment, up to two data gathering devices 50, 50′are incorporated on the backplane to monitor and control environmentalconditions in the enclosure or, in this case, one shelf in a multi-shelfenclosure.

The backplane further includes a pair of edge connectors (not shown),each adapted to receive one of a potential pair of plug-in enclosureservices processor cards 4, 4′, each including a respective processor7,7′. In the present embodiment, the processor operates according to theSCSI Enclosure Services protocol (SES) and so the cards are labelledSES₀, SES₁, although it will be seen that the invention is not limitedto this protocol. Such processors may support, for example, SCSIAccessed Fault-Tolerant Enclosure (SAF-TE), SCSI Enclosure Services(SES) or Intelligent Platform Management Interface (IPMI) enclosuremanagement protocols.

One or more of a range of SES Processor cards 4,4′ can be plugged in andpopulated to provide advanced features, such as Ethernet, Direct AttachFibre or Simple Network Management Protocol (SNMP). Where two cards areused redundancy is provided as explained below.

A further plurality of edge connectors (not shown) are mounted on thebackplane, and a set of disk drives 80 are inserted into associatedslots in the rack system where they connect at their rear to respectiveedge connectors and are thus interconnected via the backplane. The diskdrives of the preferred embodiment are Fibre Channel based disks,however, as will be seen, the invention is not limited to Fibre Channeldevices. Such disks include two pairs of fibre channel ports, each pairconnecting to a respective one of a pair of Fibre Channel-ArbitratedLoops (FC-AL) designated Loop A and Loop B. Each disk further includesan Enclosure Services Interface (ESI) port (also more properly known asSFF-8067. SFF=Small Form Factor). This is conventionally used to providecommunication between each disk and an enclosure services processorlocated on either a card connected to the backplane or even incorporatedon the backplane.

In the case of the preferred embodiment, however, two of the disk slotsin each backplane are connected via respective 4 track sets of circuittraces 52, 52′ to one of two ESI ports on each of the data gathererdevices 50, 50′. Thus the slot for Disk₀ connects to ESI₀ of both datagatherer devices 50 and 50′, and the slot for Disk₁ connects to ESI₁ ofboth data gatherer devices 50 and 50′.

Where a fibre channel medium is used, a host application (not shown)communicates with each of the disks 80 via one of the fibre channelloops. When the host application wishes to send and receive enclosureservices information, for example, using the SES protocol, it sends arequest to a pre-determined one of Disk₀ or Disk₁. When the receivingdisk processes the request, it determines that the request is anenclosure services request and forwards this request through its ESIport.

In the preferred embodiment, the ESI interfaces for the remainingDisks_(2 . . . n) connected to the backplane 10 do not connect directlyto the data gatherer devices. (N is typically 12 for a 19″ rack housing12 disks.) Without further circuitry, this forces one of the slots forDisk₀ or Disk₁ to be populated if enclosure services are to becontrolled and monitored from the host application—otherwise theenclosure services processor operates autonomously. It is nonethelesspossible to provide, for example, an additional device on the backplanewhich is connected to each of the ESI ports for Disks_(2 . . . n) andwhich multiplexes communication with these disks into a single ESI orequivalent bus connecting to either an additional port on the datagatherer devices 50, 50′ or even directly to the enclosure servicesprocessor.

In any case, each data gatherer device 50, 50′ incorporates two SerialPeripheral Interface ports SPI₀ and SPI₁. On receiving a request on anESI port, a data gatherer 50, 50′ may then communicate the request toone of the two enclosure services processors 7,7′ via one of two threewire SPI busses 54, 54′ connected to SPI₀ and SPI₁ ports respectively.Similarly, responses from the enclosure services processors 7,7′ arerelayed to the host application via the data gatherer devices 50,50′.

Each processor 7,7′ includes a further serial port (SER). The SER portsare interconnected via a two wire serial bus 56, and this is used by thetwo processors 7,7′ to arbitrate between one another as to which will beresponsible for the provision of enclosure services. In the presentembodiment, the processors communicate using an RS-232 protocol,however, only 5V signalling is used, as the 12V required by conventionalRS-232 would require an additional supply voltage to be used by theprocessors 7,7′.

The responsible processor 7,7′ can operate in one of two modes:

Standalone (autonomous) mode, where it operates alarms and LED's withoutany outside interaction other than from a mute switch (not shown) housedwithin the enclosure; or

Non-redundant mode, where it reports status to and receives commandsfrom the host application out-of-band via an RS-232 connection (notshown) or in-band via ESI (Enclosure Services Interface) for fibrechannel or directly over parallel SCSI. (In any case, if nocommunications are received from the host for a certain length of timeoperation reverts to standalone mode.)

Note that while both ESI based and parallel SCSI (hatched)communications are shown in FIG. 1, only one of these would be used inany particular product.

Where the backplane is used for parallel SCSI devices, the processors7,7′ share a SCSI identifier (or they may each have an individualidentifier) and communicate with a SCSI host application 1 directlyacross a SCSI bus 2. To enable this communication, a SCSI interface chipsocket 6 is populated—unless either standalone use or out-of-bandreporting is used. The presence of the SCSI bus on the SES processorcards 4,4′ enables the bus to be extended to a connector on the cards toallow on the one hand a computer running the SCSI host application 1 toconnect to the SCSI bus via the processor card 4 and on the other hand aterminator 58 to connect to the end of SCSI bus via the processor card4′ (or vice versa).

Again, because of the presence of the SCSI bus on the processor cards4,4′, it is also possible to incorporate a SCSI analyser 5,5′ disclosedco-pending application entitled “Performance Monitoring in a StorageEnclosure” naming Aedan Diarmid Cailean Coffey et al as inventors intothe processor card. In the present embodiment, each processor 7,7′ isconnected to a respective SCSI analyser 5,5′, via a dedicated serialconnection comprising two lines 14,15; and 14′15′. This means thatwhichever processor takes responsibility for the shelf will be reportingthe results from its associated SCSI analyser.

On the other hand, where a fibre channel medium is employed, for eachdisk 80, each of the sending and receiving ports for loop A and loop Bare brought onto processor card 4 and 4′ respectively. Conventionally aloop bypass circuit is employed to connect each disk in a loop and tobypass ports where no disk is inserted in the slot. This, however,limits the configuration of the disks in the loop to the physical orderin which they are inserted into slots in the rack.

In the preferred embodiment, however, a cross-point switch 30,30′ asdescribed in co-pending application entitled “Cross-Point Switch for aFibre Channel Arbitrated Loop” naming Aedan Diarmid Cailean Coffey asinventor is used to connect each of the disk sending ports to areceiving port of another disk in one of Loops A or B in a configurablemanner. Thus, disks (or repeaters or retimers if necessary) may beordered in either loop in any desirable manner and furthermore, they maybe spaced apart in the loop in a manner that smoothes the signal levelthroughout the loop. It should also be seen that because each disksending and receiving port in a Loops A and B are connected torespective processor cards 4,4′, it is possible to include one or twoFibre-Channel Analysers 70,70′ as described in copending applicationentitled “Fibre Channel Diagnostics in a Storage Enclosure” naming AedanDiarmid Cailean Coffey et al as inventors on the processor cards 4,4′.

A further advantage to using a cross-point switch is that the fibrechannel analysers can be connected to the fibre channel Loops A and Bbut need not be in the loops in the manner of a fibre channel device, soaffecting the operation of the loop they are analysing.

In order to configure the cross-point switches 30,30′, the processor7,7′ responsible for the shelf needs to determine which disks arepresent. In common with all other devices plugged into the backplane,each disk 80 includes a present output P. Each present output P isconnected to one of a series of Pres_(1 . . . m) inputs (where m isgreater than the number of disks N) on each of the data gatherer devices50,50′. Whichever of the data gatherers 50,50′ is enabled (explainedlater) reports which disk slots are occupied to the responsibleprocessor 7,7′ via its SPI port connecting the gatherer 50,50′ to theresponsible processor 7,7′. Both the processors 7,7′ and the cross-pointswitches 30,30′ include respective serial ports inter-connected via anI²C bus. The I²C bus also extends across the backplane to in turninter-connect the processors and switches via the backplane allowingeach cross-point switch 30,30′ to be addressed from either processor7,7′.

The responsible processor 7,7′ can thus determine the switches which areto be closed to link each of the disks 80 in respective Loops A and Band relays this information to the cross-point switches 30,30′ via theI²C bus.

If the responsible processor 7,7′ is in communication with a hostapplication, then the operator using the host application may specifywhere in the Loops A or B, the fibre channel analysers 70,70′ are to belocated. On receiving such a request the responsible processor 7,7′again determines which further cross-point switches are to be closed tolocate the fibre channel analysers in either of Loops A or B and this isrelayed to the appropriate cross-point switch 30,30′ via the I²C bus. Asdescribed in co-pending application entitled “Fibre Channel Diagnosticsin a Storage Enclosure” naming Aedan Diarmid Cailean Coffey et al asinventors each analyser 70,70′ is connected via a respective bus to aport on the processor 7,7′. Data returned from the analysers 70,70′ canonly be collated by the responsible processor 7,7′ and returned to thehost application as required. Thus, if the host application specificallywishes analysis of the loop connected to the non-responsible processorcard 4,4′, it must instruct the responsible processor to transferresponsibility to the other processor, if this is possible.

Reverting now to the operation of the processors 7,7′, once arbitrationis complete and a responsible processor determined, the responsibleprocessor 7,7′ then instructs an associated data gatherer device 50,50′to in turn take responsibility for the gathering of input data and thecontrol of enclosure outputs.

In the present example, processor 7 is associated with data gathererdevice 50 and processor 7′ is associated with data gatherer device 50′.SPI₀ on each data gatherer 50,50′ is connected via busses 54,54′ to theSPI port on its associated processor 7,7′, whereas SPI₁ iscross-connected to the other of the processors SPI port again via busses54,54′.

If, for example processor 7 takes responsibility, by default, processor7′ and data gatherer 50′ go into a “dead till enabled” standby mode. Inthis case, SES requests sent from either of Disk₁ or Disk₀ are receivedand forwarded by data gatherer 50. If the data gatherer 50 is beingcontrolled by its default processor 7, then it relays the SES requestvia port SPI₀ to the processor 7.

If processor 7 for some reason fails, then the other processor 7′ andits associated data gatherer 50′ will take over responsibility forenvironmental monitoring. In the preferred embodiment, each processor7,7′ and data gatherer device 50, 50′ includes a watchdog timer which,if it detects failure of its controlling device, should cause the deviceto take itself out of service.

As an additional measure each processor 7 includes an input and outputreset port RST_(I) and RST_(O) respectively, each data gatherer deviceincludes an RST_(I) port and each SCSI Interface chip includes an inputreset port (not labelled). The RST_(O) port of the processor 7 isconnected to the RST_(I) ports of the processor 7′, the data gatherer50′ and the SCSI I/F chip 6′ and vice versa. This enables either theprocessor 7 or 7′ to force the backplane electronics into reset if itthinks that the other processor, its associated gatherer device or wherepopulated the SCSI I/F may be causing the backplane to fail.

It will be seen that in the case of failure of one of processors 7,7′and/or one of gatherers 50, 50′, the host application, although it canbe notified of the failure, will not be affected, as it can still sendits requests via the same disk from which the requests will be picked upby data gatherer 50′ and relayed to processor 7′.

If a situation occurs where, say processor 7 and data gatherer 50′ fail,then it will be seen that processor 7′ will again take overresponsibility, however, when it instructs a data gatherer that it hasresponsibility, the instruction will be picked up by data gatherer 50through its port SPI₁ and data gatherer 50 will assume responsibility.Again, the host application will be unaffected, and so it will be seenthat from host to enclosure services processor, eight possible pathsexist, with no single point of failure on these paths, and with thisarrangement each processor 7,7′ can control it's own and the otherprocessor's access to the SPI busses 54,54′.

Nonetheless, while the preferred embodiment shows two data gathererdevices included on the backplane, this level of redundancy may not berequired by some and it will be seen that if only one device 50, 50′ isprovided on the backplane, then this will be detected by whichever of upto two plugged-in processors 7,7′ gets control of the backplane, and itwill simply operate with a potential single point of failure on thebackplane.

Turning now to the type of data monitored and controlled by theprocessors 7,7′. In the preferred embodiment, as well as the presentinputs Pres_(1 . . . n) received from the disks 80, each other deviceconnected to the backplane has a present (or equivalent) output P whichis connected to a respective one from the remainder of thePres_(1 . . . m) inputs on each of the data gatherer chips 50,50′.

In the present embodiment, these devices include two power supply unitsPSU₀ and PSU₁ for each shelf whose operation is described in co-pendingapplication entitled “A Protocol for a Power Supply Unit Controller”naming Barrie Jeremiah Mullins et al as inventors; and co-pendingapplication entitled “Improved Power Supply Unit Controller” namingBarrie Jeremiah Mullins et al as inventors.

Data is gathered by the processor 7,7′ directly from respectivecontrollers within the power supplies via the same I²C bus connectingthe processors 7,7′ to the cross-point switches 30,30′. Each powersupply's P output represents a PSU_OK signal which indicates to the datagatherer 50,50′ both that the PSU is present and that it is operatingcorrectly in all ways. If the I²C bus fails, the PSU_OK signals canstill be monitored through the data gatherers 50,50′ but detailedinformation cannot be read. Thus it is possible to identify a failingPSU, but not to diagnose the failure. In the meantime, the PSU firmwareoperates in autonomous mode and set it's fault LED.

In any case, the data gathering device autonomously controls delayedspinup of the disks—fibre channel or parallel SCSI—based on the twopower supplies reporting themselves as present and working OK, thusavoiding any timing issues regarding how soon delayed_spinup signals(not shown) must be asserted after power up. On power up both datagathering devices remain inactive (i.e. all outputs tristate, exceptdelayed_spinup) until enabled by the responsible processor 7,7′.Alternatively, if the power supplies are powerful enough to supportspinning up all the disks at the same time, there is no need toimplement a delayed spinup system.

Each PSU further includes a thermometer (not shown) which is alsoconnected to and addressable on the I²C bus. Further thermometersTherm₀, Therm₁ and Therm₂ are located on the backplane, processor card 4and processor card 4′ respectively and connect to and are independentlyaddressable on the I²C bus by whichever processor 7,7′ hasresponsibility for the shelf.

Each shelf also includes two advanced cooling modules (ACM₀ and ACM₁)each including 2 fans Fan₀ and Fan₁. In the preferred embodiment, theseare conventional style modules whose fan speed is measured andcontrolled through respective input/output ports ACM₀ and ACM₁ on eachof the data gatherers 50,50′. Again these modules include a presentoutput P connected to respective Pres inputs on each of the datagatherers 50,50′. In an alternative embodiment, the ACMs could alsoinclude controllers corresponding to those of the PSUs and be directlyaccessible to the processors 7,7′ via the I²C bus. This would obviatethe need for the input/output lines on the data gatherer 50,50′ withoutrequiring further pins on the processor card 4,4′ edge connector. Againin this case, if the I²C bus is brought down then the fans operate inautonomous mode. If they detect a failure they set their error LED's(not shown) but the host, via the processor 7 or 7′, will not know aboutit.

Each data gatherer 50,50′ also includes at least 37 LED outputsLED_(0 . . . x) (3 LEDS for 12 disk drives plus one fault LED). Thebackplane also includes miscellaneous LED's LED_(1 . . . y) which arecontrolled from respective outputs of the outputs LED_(0 . . . x). Eachgatherer further contains a programmable LED flash generator to allowcustomisation for various LED flash patterns.

Data from all other inputs is gathered directly via either other Presinputs or general purpose inputs (not shown) on the data gatherers50,50′. The responsible data gatherer 50, then makes this data availableto the responsible processor 7,7′ via the appropriate SPI bus 54,54′.These general purpose input and also output pins also allow the hardwareto operate with additional features of future backplane releases bysimply upgrading gatherer software.

The data gathering device has several features to accommodateredundancy, such as:

All control outputs being open drain to prevent damage in the event thatboth data gathering devices get enabled at the same time;

All outputs being held in tri-state if the reset pin is asserted; and

All outputs except delayed_spinup being held in tri-state once reset isdeasserted until a specific command has been received to enable them.

It is acknowledged that in the present embodiment, since power suppliesand possibly ACMs only have one I²C interface there cannot be fullredundancy in the monitoring system. Thus, there exists a possibility ofa faulty device such as a microcontroller, fan, power supply, etc.bringing the main I²C bus down and disabling all communications.Although the invention is not limited to such a single bus, nonetheless,in the single bus case, the data gatherer can still receive thehardwired present outputs and the devices themselves can autonomouslyset any of their on-board error LED outputs or buzzers.

In the case of the two SPI interfaces on the data gathering chip, theseoperate independently such that a failure on one will not result in afailure on the other. Since a high degree of reliability can be expectedof the data gathering device and since it is independent of the main I²Cbus, it can thus be used to control segmentation of the I²C bus toremove faulty devices.

While the preferred embodiment has been described in terms of specificbusses, it will be seen that any bus can be replaced by any functionallyequivalent bus, serial or parallel, according to the performancerequirements of the system. So for example, the I²C bus could bereplaced with a faster three wire serial bus (SPI bus).

Other features of the data gatherers which, although not required by theinvention, could be included are:

General inputs to support product ID, shelf ID or cabinet ID; and

Support for one or more buzzers (with programmable beep patterns).

So, it will be seen that a data gatherer chip equally useful eitherindividually or in a pair on any backplane with complaint tracking isprovided by the invention. The chip in turn operates with an enclosureservices processor, again equally useful either individually or as oneof a pair, within one of a range of processor cards again with complianttracking which can be selectively populated to provide desiredfunctionality.

In both cases designing for example parallel SCSI or fibre channelversions of the card 4,4′ or backplane 10 with compliant trackingenables the same chips 7,7′,50,50′ to be used, so reducing developmentoverhead. This simply means that where, for example, the data gathereris used for parallel SCSI, the ESI ports do not receive signals.Similarly, where the processor 7,7′ is used for fibre channel, the SCSIanalyser and SCSI interface ports do not receive signals. Again, wherethe processor 7,7′ is used for parallel SCSI, the fibre channel analyserports do not receive signals and neither would a cross-point switch beaddressable on the I²C bus.

What is claimed is:
 1. A data gathering device for a rack enclosure which is, in use, cooperable with at least one environmental services processor, each processor being incorporated in a respective plug-in card, said data gathering device comprising at least one port adapted to communicate with a respective environmental services processor, a plurality of data inputs and a plurality of controllable outputs, said data gathering device being adapted to generate and send, to a one of said at least one environmental services processors responsible for said enclosure, a message reporting the state of said data inputs and to receive, from said responsible environmental services processor, a message including a command determining the state of one of said controllable outputs, wherein said data gathering device includes two ports, each adapted to communicate with a respective one of two environmental services processors.
 2. A backplane for a rack enclosure, said backplane including one or more data gathering devices, each data gathering device being, in use, cooperable with at least one environmental services processor, each processor being incorporated in a respective plug-in card, each data gathering device comprising at least one port adapted to communicate with a respective environmental services processor, a plurality of data inputs and a plurality of controllable outputs, each data gathering device being adapted to receive an instruction from a one of said at least one environmental services processors responsible for said enclosure to take responsibility for data gathering, said data gathering device being adapted, when responsible for said enclosure, to generate a message reporting the state of said data inputs to said responsible environmental services processor and to receive a message including a command from said responsible environmental services processor determining the state of one of said controllable outputs, wherein the backplane is adapted to receive two enclosure services cards, each connected to a respective data gatherer device and cross-connected to another data gatherer device.
 3. A backplane according to claim 2 wherein the backplane is adapted to receive fibre channel storage devices and said data gathering device includes at least one port adapted to communicate with a respective one of said storage devices, said data gathering device being adapted to relay environmental services requests from a host application received via a storage device to said responsible environmental services processor and to relay responses from said responsible environmental services processor to said storage device. 